Method and apparatus for downhole spectral analysis of fluids

ABSTRACT

A downhole fluid analysis system comprises an input light signal that is directed through a fluid sample housed in a sample cell. The input light signal may originate from a plurality of light sources. A light signal output from the sample cell is then routed to two or more spectrometers for measurement of the represented wavelengths in the output light signal. The output of the spectrometers is then compared to known values for hydrocarbons typically encountered downhole. This provides insight into the composition of the sample fluid. Additionally, the input light can be routed directly to the two or more spectrometers to be used in calibration of the system in the high temperature and noise environment downhole.

FIELD OF THE INVENTION

The present invention relates to methods and apparatus for fluidanalysis using a spectrometer architecture downhole in subterraneanformation evaluation and testing for the purpose of exploration anddevelopment of hydrocarbon-producing wells, such as oil or gas wells.More specifically, a fluid analysis module with at least twospectrometers is used in characterizing downhole fluid.

BACKGROUND OF THE INVENTION

In order to evaluate the nature of underground formations surrounding aborehole, it is often desirable to obtain and analyze samples offormation fluids from a plurality of specific locations in the borehole.Over the years, various tools and procedures have been developed tofacilitate this formation fluid evaluation process. Examples of suchtools can be found in U.S. Pat. No. 6,476,384 (“the '384 patent”),assigned to Schlumberger Technology Corporation (“Schlumberger”). Thedisclosure of this '384 patent is hereby incorporated by reference asthough set forth at length.

Schlumberger's Repeat Formation Tester (RFT) and Modular FormationDynamics Tester (MDT) tools are specific examples of sampling tools asdescribed in the '384 patent. In particular, the MDT tool includes afluid analysis module for analyzing fluids sampled by the tool.

Over the years, various fluid analysis modules have been developed foruse in connection with sampling tools, such as the MDT tool, in order toidentify and characterize the samples of formation fluids drawn by thesampling tool. For example, Schlumberger's U.S. Pat. No. 4,994,671 (alsoincorporated herein by reference) describes an exemplary fluid analysismodule that includes a testing chamber, a light source, a spectraldetector, a database, and a processor. Fluids drawn from the formationinto the testing chamber by a fluid admitting assembly are analyzed bydirecting light at the fluids, detecting the spectrum of the transmittedand/or backscattered light, and processing the information (based oninformation in the database relating to different spectra) in order tocharacterize the formation fluids. Schlumberger's U.S. Pat. No.5,167,149 and U.S. Pat. No. 5,201,220 (both of which are incorporated byreference herein) also describe reflecting light from a window/fluidflow interface at certain specific angles to determine the presence ofgas in the fluid flow. In addition, as described in U.S. Pat. No.5,331,156, by taking optical density (OD) measurements of the fluidstream at certain predetermined energies, oil and water fractions of atwo-phase fluid stream may be quantified. As the techniques formeasuring and characterizing formation fluids have become more advanced,the demand for more precise and expandable formation fluid analysistools has increased.

Prior optical fluid analysis tools typically utilized a single lightsource directed at a sample cell and a single spectrometer to collectand analyze the light. In a typical embodiment, a filter array (FA)spectrometer is used which provides a maximum of about 20 channels.These tools are used downhole in adverse conditions which can affect thesignal to noise ratio of the spectrometer.

The prior approaches while being largely effective also exhibit certainlimitations. While the measurements from the single FA spectrometer areuseful, it is desirable to have a system where multiple spectrometers ofdifferent types can be utilized downhole at the same time to analyzefluid. This would alleviate the need for multiple separate modules; asingle light source may provide information to a group of differentspectrometers increasing the number of channels available and thespecificity of the overall system.

Adverse conditions downhole also make it necessary to calibrate aspectrometer system such as those in the prior art. This requiresdirecting at least two beams of light, one reference signal and onemeasurement signal, at a spectrometer. This requires differentiation oflight signals which can be achieved through the use of a light chopper,as disclosed in co-pending U.S. patent application Ser. No. 11/273,893relating to real-time calibration for a downhole spectrometer. However,light choppers require a motor that increases the size of the downholetool significantly.

SUMMARY OF THE INVENTION

In consequence of the background discussed above, and other factors thatare known in the field of downhole fluid analysis, applicants recognizeda need for an apparatus and method for broad spectral optical analysiswhile providing detailed spectral analysis in a range of interest. Inthis, applicants recognized that a spectral analysis system that isconfigured with a plurality of spectrometers, which are selected basedupon the needs and requirements of the spectral analysis to beundertaken, would provide significant improvements in the accuracy andefficiency of downhole fluid analysis.

One embodiment of the invention comprises a method and apparatus forfluid analysis downhole using a spectrometer. In one aspect, one or morelight sources are directed at a sample cell that contains fluidextracted downhole. The light transmitted through the sample is measuredby two or more spectrometers for spectral analysis of the fluid.Additionally, light from the one or more light sources is routeddirectly to the same set of spectrometers to provide a referencemeasurement used in calibration. Two or more different types ofspectrometers may be used, including, but not limited to, filter arrayand grating spectrometers.

Additional advantages and novel features of the invention will be setforth in the description which follows or may be learned by thoseskilled in the art through reading the materials herein or practicingthe invention. The advantages of the invention may be achieved throughthe means recited in the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate preferred embodiments of thepresent invention and are a part of the specification. Together with thefollowing description, the drawings demonstrate and explain principlesof the present invention.

FIG. 1 is a schematic view of one exemplary context in which the presentinvention may be used.

FIG. 2 is a schematic partial cross-sectional view of one exemplarystructure of a fluid analysis module according to the present invention.

FIG. 3 is a cross-sectional schematic view of one filter channel in alarger filter array type spectrometer.

FIG. 4 is an illustrative representation of the absorption spectra of anumber of hydrocarbons encountered downhole.

FIG. 5 is a schematic representation of one exemplary structure of amethod and apparatus according to the present invention where light frommultiple sources is routed to a plurality of spectrometers.

FIG. 6 is a schematic representation of one embodiment of a spectralanalysis system according to the present invention.

FIG. 7 is a cross-sectional schematic of an exemplary sample cell in onedownhole implementation of a spectral analysis system according to thepresent invention.

FIG. 8 is a schematic of another embodiment of a spectral analysissystem according to the present invention.

Throughout the drawings, identical reference numbers indicate similar,but not necessarily identical elements. While the invention issusceptible to various modifications and alternative forms, specificembodiments have been shown by way of example in the drawings and willbe described in detail herein. However, it should be understood that theinvention is not intended to be limited to the particular formsdisclosed. Rather, the invention is to cover all modifications,equivalents and alternatives falling within the scope of the inventionas defined by the appended claims.

DETAILED DESCRIPTION

Illustrative embodiments and aspects of the invention are describedbelow. In the interest of clarity, not all features of an actualimplementation are described in the specification. It will of course beappreciated that in the development of any such actual embodiment,numerous implementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, that will vary from one implementation toanother. Moreover, it will be appreciated that such development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having benefit of thedisclosure herein.

FIG. 1 is a schematic diagram of an exemplary downhole tool 110 fortesting earth formations and analyzing the composition of fluids fromthe formation. Downhole tool 110 is suspended in a borehole 112 from acable 115 that is connected in a conventional fashion to a surfacesystem 118. Surface system 118 incorporates appropriate electronics andprocessing systems for control of downhole tool 110 and analysis ofsignals received from the downhole tool.

Downhole tool 110 includes an elongated body 119, which encloses adownhole portion of a tool control system 116. Elongated body 119 alsocarries a selectively-extendible fluid admitting/withdrawal assembly 120and a selectively-extendible anchoring member 121. Examples of the fluidadmitting/withdrawal assembly are shown and described, for example, inSchlumberger's U.S. Pat. No. 3,780,575, U.S. Pat. No. 3,859,851, andU.S. Pat. No. 4,860,581. The disclosure of each of these patents isincorporated herein by reference. Fluid admitting/withdrawal assembly120 and anchoring member 121 are respectively arranged on opposite sidesof the elongated body 119. Fluid admitting/withdrawal assembly 120 isequipped for selectively sealing off or isolating portions of the wallof borehole 112, such that pressure or fluid communication with theadjacent earth formation can be selectively established. A fluidanalysis module 125 is also included within elongated body 119 andformation fluid to be analyzed is channeled through the analysis module.The sampled fluid may then be expelled through a port (not shown) backinto borehole 112, or sent to one or more sample chambers 122, 123 forrecovery at the surface. Control of fluid admitting/withdrawal assembly120, fluid analysis module 125, and the flow path to sample chambers122, 123 is maintained by electrical control systems 116, 118.

FIG. 2 shows one example of a spectral analysis module 134 that may beintegrated into the tool 110. The formation fluid 132 is the sample ofinterest to the end user of the system. This fluid may contain anynumber of components including, but not limited to, gas, oil, and water.As mentioned above, it is highly desirable to know what fluids arepresent and in what relative quantities. To accomplish this, lightsource 130 is positioned to direct light toward one of the two opticalwindows 136. In one embodiment of the present invention, this light maybe a halogen lamp, a light emitting diode (LED), a laser, or any otherlight source that can be introduced downhole. These light sourcesproduce light across a wide spectral range, approximately 500-2000 nm inwavelength. The light produced by light source 130 is transmittedthrough the first optical window 136, through the sample fluid 132 andemerges from the second optical window 136. This light is collected andtransmitted using fiber optic bundles which allows for the specificdirection and routing of the light signals. The light of particularinterest is that which is reflected, transmitted and/or emitted, i.e.,the output light, from the sample fluid. This output light signal isdirected (again, usually using fiber optics) to a spectrometer section138 of the spectral analysis module. In prior systems, the spectrometersection typically contained a single FA spectrometer with a maximum of20 channels. In one embodiment, the instant invention provides for aplurality of spectrometers to be included in the spectrometer section138. This increases the number of available channels and also allows fora different type of spectrometer, such as a grating spectrometer, to beincluded in the detection and analysis of the output light signal. Theoutput of the spectrometer section is used in determining thecharacteristics of the sample fluid 132.

FIG. 3 is a schematic view of one of the channels of an FA spectrometerthat is typically used in prior systems and may be used as one of thespectrometers in the instant invention. Light is input at 140 via afiber optic bundle which allows the light to be routed to each of thechannels through multiple paths labeled 142. One of those paths willdeliver a light signal to input fiber bundle 144. This light thentraverses through first lens 146 and through filter 148. Filter 148 istypically a bandpass filter. This bandpass filter will only allow lightin a range of wavelengths to pass. The full spectrometer has a pluralityof these filter elements, each of which may correspond to a differentband of wavelengths. After moving through filter 148, the signal isrefocused by the second lens 146 toward the output photodetector 150.This photodetector generates a current based on incident light with thecurrent being proportional to the amount of incident light. This currentis then converted to a voltage by I/V converter 152 and the voltagesignal moves on for further processing. As can be seen, the voltage willdiffer for each tested wavelength and give an indication of the relativecontributions of the different wavelengths. Based on control data, thiswill give insight to the composition of the sample fluid.

Optical absorption is wavelength dependent and is determined by thesample fluid composition. FIG. 4 shows the absorption characteristics ofseveral hydrocarbons and other fluids that will likely be encountereddownhole. Axis 162 is the wavelength of light transmitted and axis 160is the corresponding optical density (OD). Water is shown by line 164,element 166 corresponds to diesel, element 168 corresponds tocondensate, element 170 corresponds to oil based mud filtrate, element172 corresponds to crude A, and element 174 corresponds to crude B.Several spectral regions can be discriminated and these regions giveinsight into the composition of the overall fluid. It is shown here thatwater peaks at about 1450 nm, just before a region of high interestwhere a number of hydrocarbons peak. Between 1.6 μm and 1.8 μm, theregion labeled 176, hydrocarbons have strong absorption and show manyspectral dependent features that must be detected. However, due to thelimited number of channels of an FA spectrometer, it is not possible tocapture all the spectral details. The FA spectrometer covers fromvisible to IR range, this invention allows for a hybrid spectrometerarchitecture to add greater channel density in specific spectralregions.

Turning now to FIG. 5, in the instant invention, two or morespectrometers are introduced downhole. In one embodiment of the presentinvention, at least one of the spectrometers may be an FA spectrometerand at least one may be a grating spectrometer. For example, the gratingspectrometer may be configured to provide very high channel density in alimited range of wavelengths. It is useful in measuring spectral detailsin the important 1.6-1.8 μm range labeled 176. For example, the gratingspectrometer may be configured to provide approximately 16 channels;these channels are in addition to the 10-20 channels provided by the FAspectrometer and provide more specific information about a smallerspectral range. For example, the FA spectrometer may be configured tomeasure in the visible and infrared range to determine the presence offluids, such as water which has a peak at 1450 nm, and for baselinecorrections, while the grating spectrometer may be configured to monitorthe hydrocarbon range mentioned above. Other combinations ofspectrometers are contemplated by the present invention such that a widerange of wavelengths are available for spectral analysis of downholefluids. Spectral features in the visible range are limited, so the highchannel density of the grating spectrometer is not as much of anecessity.

A schematic of one embodiment of the invention is shown in FIG. 5. Inputlight is provided by light source 180. As shown, there may be aplurality of different types of light produced at the light source.These include, but are not limited to, a halogen bulb (broad band lightsource), a light emitting diode (LED), and a laser. This input light maybe processed by one of the light processing units 188. These lightprocessing units may include any unit for changing a property of light,such as polarizer, amplitude and frequency modulators, among other lightprocessing units. In one embodiment, the light then may be introduced tolight collector 182 although this element is optional depending on thenumber of light sources and spectrometers in operation. This lightcollector is configured to allow light of different wavelengths to berouted to different locations or at different times. This is useful whenit is desired to determine the affects of different light typesindependently. The input light then proceeds to one or more inputwindows of sample cell 184. This sample cell houses fluid flowingthrough the flowline which is the sample fluid to be tested. The lightflows through the fluid and undergoes interactive change depending onthe wavelength of the light and the composition of the fluid to producean output light. For example, the input light may undergo reflectionand/or absorption and/or light may be emitted as a result of interactionbetween the input light and the sample in the flowline. In this, thepresent invention contemplates a variety of known methodology forspectral analysis of fluids.

The output light traverses through an output window of the sample cell184 and on to an optional light collector and router 182. The light isthen routed to one of a plurality of spectrometers 186. As mentionedabove, in one embodiment of the present invention, at least one of thesemay be an FA spectrometer and at least one of these may be a gratingspectrometer. The output of these spectrometers, as mentioned above,will show the amounts of sample cell output light in a set of wavelengthranges.

In addition to the light incident on the sample cell, it is alsoadvantageous to route light directly from the one or more light sources180 to the plurality of spectrometers 186. The light sources,photodetectors, and processing electronics employed in conventionalfluid analysis modules are typically adversely affected by the extremetemperatures and vibrations experienced downhole. For example, theoptical power of light sources tends to diminish or drift when operatedat elevated temperatures. Similarly, the optical gains of manyphotodetectors may drift by significant amounts when subjected to thesehigh operating temperatures. These shifts may result in improperresults, but calibration can be accomplished while testing to compensatefor this drift. This calibration is accomplished by continuouslydirecting light from the light sources 180 to the spectrometers 186. Toaccomplish this, light from the one or more light sources 180 is routed,via a fiber optic bundle, through optional light collector 183 and thenon to the plurality of spectrometers 186. This light signal is referredto as the reference light signal, the light directed through sample cell184 is referred to as the measurement light signal.

For calibration to be successful, it is necessary for the referencelight signal and the measurement light signal to be separated before orat the plurality of spectrometers. This is because the spectrometerswill detect all incident light, so for the signals to be compared, theremust be some difference. In one embodiment, this differentiation may beperformed by light processing units 188. These may include frequencymodulators such as an optical chopper wheel. A chopper wheel is a discthat includes a set of openings that the light signal is directedtoward. Based on the size of the openings, the light is transmitted at acertain frequency. The reference signal and the measurement signal aretransmitted as different signals that can be determined so which signalis being measured by the spectrometers is known. The reference signal isthen used in calibration while the measurement signal is used todetermine the composition of fluid in the sample cell 184. Co-pendingU.S. patent application Ser. No. 11/273,893 (incorporated herein byreference in its entirety) discloses real-time calibration for adownhole spectrometer.

FIG. 6 is a schematic representation of one spectral analysis systemaccording to the present invention. Light is introduced by input light200. Again, this may be a plurality of light sources depending on theapplication. The light is then split into two paths. The first is themeasurement path and the light traverses through sample cell 202. Thissample cell houses the downhole fluid that is to be analyzed. The secondpath is the reference path. Both paths then intersect with the rotatingchopper wheel 208 at different points on the wheel. This wheel may berotated by motor mechanism 204. This causes the frequency of each of thelight signals to be modulated independently. The measurement lightsignal at point 206 has a first frequency and is split into two paths.The reference light signal at point 210 has a second frequency and issplit into two paths. These light signals are then routed to thespectrometers. The first spectrometer 214 may be an FA spectrometer asdescribed above. The second spectrometer 216 may be a gratingspectrometer. The light signals first pass through spectrometer input218. This input also functions as a long pass filter for the lightsignals. Once inside grating spectrometer 216, the light is reflectedoff mirror 220 and eventually to the output of the grating spectrometer.A photodetector 222 is positioned at the output of the gratingspectrometer to measure the light output and convert it to a currentproportional to the amount of output light. This current is thenconverted to a voltage by I/V converter 224 and then passed on forfurther analysis. Photodiodes 212 are used in the synchronization of thesignal before and after the chopper wheel.

FIG. 7 is a cross sectional view of one embodiment of a sample cell suchas described in the previous figures. The depicted embodiment of theinvention may be implemented in a plurality of other configurations. Thesample fluid flows through flow channel 234. Opposed openings 236 and240 are provided in the flowline each of which interfaces with an inputor an output window and flange assemblies, respectively. Structurally,the input and output sides of the cell are identical, so only the inputside will be described in detail. Flow channel 234 is located betweenopenings 236 and 240 and defines window locating seats. Windows 242 arelocated on each side of the flow channel 234. In one embodiment, thewindows may be made of sapphire. The windows 242 are secured in place byflanges 230 which are provided with optical connectors to connect theouter faces of the windows 242 with fiber bundles 232 and 244. Theflanges may be screwed to each other so as to seal the windows into theseats. Sealing is assisted by the use of back up rings and O-rings 238.Inner and outer faces of the windows 242 are polished to opticalquality, side faces are polished to assist in sealing.

FIG. 7 depicts just one sample cell with a single set of windows. Theremay be additional windows and fiber bundles that direct different typesof light to different locations all traversing through the sample fluid.The light input through fiber bundle 232 interacts with the sample fluidand the output light is collected by fiber bundle 244. This receivedlight signal is then forwarded on to the plurality of spectrometers foranalysis.

FIG. 8 is a schematic representation of one embodiment of an overallstructure for a spectral analysis system according to the presentinvention. Light source 250 passes light through a chopper wheel 254driven by a chopper motor 252 into an optical fiber bundle 256. Outputsare taken from bundle 256 to provide input to a motor synchronizationphotodiode 258, a source light input path 282, a light distributor 286(forming part of the detector described in more detail below) and to ameasure path 264 which provides input to the spectrometer cell 270. Acalibration wheel 260 driven by a rotary solenoid switch 262 selectswhether light passes into the source light input path 282, the measurepath 264, or both. The input fiber bundle 266 connects to the inputflange 268 of the cell and optically connects to the window 272. Lightis transmitted from the window 272, across the flow path 274 throughanother window 272 and into an output fiber bundle 278 connected to theoutput flange 276. The output bundle also connects to the lightdistributor 286. The light distributor 286 distributes the lightreceived from the source light input 250 and the output fiber bundle 278to a plurality of different channels. For the purpose of this example,only four channels are shown but up to twenty may be available. This isa FA spectrometer described above that provides information on theoutput wavelengths from the sample fluid. Each channel comprises lens288 and bandpass filter 290 feeding to a photodiode 292. The filters maybe chosen to select predetermined wavelengths of light and provide anoutput signal relative to the wavelength in question. In addition to theFA spectrometer, a grating spectrometer 294 may also be provided. Path280 is routed to the grating spectrometer 294. Path 280 is the referencesignal that is provided directly from the light source to thespectrometer to be used in calibration. Path 284 is split from theoutput signal after the input light has been passed through the fluidsample. The light signal carried in path 284 is the measurement lightsignal and it is introduced to grating spectrometer 294.

The output of both spectrometers is then used in analysis of the fluidsample. The electrical outputs of the spectrometers are proportional tothe light of a given wavelength range that is incident on thespectrometers. This invention provides a large number of channelscovering a wide range of wavelengths all of which can be accomplisheddownhole in either a wireline or logging-while-drilling (LWD) ormeasurement-while-drilling (MWD) or production logging or permanentmonitoring of a well type tools. Moreover, the present inventioncontemplates applicability in areas such as carbon-di-oxidesequestration and water reservoir management. In this, it iscontemplated that the systems and methods disclosed herein will havewide ranging applications in a variety of downhole fluid analysisoperations that employ conventional spectral analysis systems fordownhole applications.

In the systems and methods disclosed herein, light from one or morelight sources 180 is directed at a sample cell 184 to interact with asample fluid therein, and output light is collected in fiber bundles androuted to two or more spectrometers 186. For example, a filter arrayspectrometer may be configured to provide information over a widespectral range, a grating spectrometer may be configured for a fineranalysis of a smaller range of wavelengths that are of special interestin determining the presence of desired hydrocarbons.

In addition to one function of measurements of light received from asample fluid, light may also be routed directly from the light sourcesto the two or more spectrometers. This reference signal is used incalibration of the spectrometers and associated electronics as theirperformance may change in the high temperature and noise environmentdownhole.

The preceding description has been presented only to illustrate anddescribe the invention and some examples of its implementation. It isnot intended to be exhaustive or to limit the invention to any preciseform disclosed. Many modifications and variations are possible in lightof the above teaching.

The preferred aspects were chosen and described in order to best explainprinciples of the invention and its practical applications. Thepreceding description is intended to enable others skilled in the art tobest utilize the invention in various embodiments and aspects and withvarious modifications as are suited to the particular use contemplated.It is intended that the scope of the invention be defined by thefollowing claims.

1. A fluid analysis system configured to operate downhole in a welltraversing a formation comprising: at least one light source generatingan input light across a wide, continuous spectral range; a sample celloperable to receive a flowing sample fluid therein, said sample cellfurther comprising: at least one input window allowing said input lightto flow into said sample cell and through the flowing sample fluid toproduce an output light; at least one output window allowing said outputlight to flow out of said sample cell; two or more downholespectrometers configured to measure said output light and generate aplurality of measurement signals; and an analysis device configured toreceive said plurality of measurement signals and determine propertiesof the flowing sample fluid.
 2. The fluid analysis system configured tooperate downhole as defined in claim 1 further comprising: a pluralityof light sources wherein said plurality of light sources generate lightacross a wide spectral range.
 3. The fluid analysis system configured tooperate downhole as defined in claim 1, wherein one of said two or morespectrometers comprises a filter array spectrometer.
 4. The fluidanalysis system configured to operate downhole as defined in claim 1,wherein one of said two or more spectrometers comprises a gratingspectrometer.
 5. The fluid analysis system configured to operatedownhole as defined in claim 1, wherein said two or more spectrometerscomprise at least one filter array spectrometer and at least one gratingspectrometer.
 6. The fluid analysis system configured to operatedownhole as defined in claim 1, wherein said at least one light sourcecomprises a halogen lamp.
 7. The fluid analysis system configured tooperate downhole as defined in claim 1, wherein said at least one lightsource comprises a light emitting diode (LED).
 8. The fluid analysissystem configured to operate downhole as defined in claim 1, whereinsaid at least one light source comprises a laser.
 9. The fluid analysissystem configured to operate downhole as defined in claim 1 furthercomprising: a plurality of light processing units for processing saidinput light and said output light.
 10. The fluid analysis systemconfigured to operate downhole as defined in claim 1 further comprisingat least one of: a first light collector positioned between said atleast one light source and said sample cell; and a second lightcollector positioned between said sample cell and said two or morespectrometers.
 11. The fluid analysis system configured to operatedownhole as defined in claim 10, wherein said first and second lightcollectors further comprise a router configured to selectively routelight to at least one of a specific input window, a specificspectrometer, and at a specific time.
 12. The fluid analysis systemconfigured to operate downhole as defined in claim 9, wherein saidplurality of processing units comprises at least one amplitudemodulator.
 13. The fluid analysis system configured to operate downholeas defined in claim 9, wherein said plurality of processing unitscomprises at least one frequency modulator.
 14. A fluid analysis systemconfigured to operate downhole in a well traversing a formationcomprising: at least one light source generating an input light across awide, continuous spectral range; a sample cell operable to receive asample fluid therein, said sample cell further comprising: at least oneinput window allowing said input light to flow into said sample cell andthrough the sample fluid to produce an output light; at least one outputwindow allowing said output light to flow out of said sample cell; twoor more downhole spectrometers configured to measure said output lightand generate a plurality of measurement signals; an analysis deviceconfigured to receive said plurality of measurement signals anddetermine properties of the sample fluid; and a reference lightcollector positioned between said at least one light source and said twoor more spectrometers, said reference light collector operable to routesaid input light directly from said at least one light source to saidtwo or more spectrometers for a reference measurement.
 15. The fluidanalysis system configured to operate downhole as defined in claim 14further comprising: one or more light processing units between saidreference light collector and said two or more spectrometers.
 16. Amethod for downhole fluid analysis comprising: providing input lightusing at least one light source generating an input across a wide,continuous spectral range; inserting a flowing sample fluid into asample cell; introducing said input light to an input window of saidsample cell, said light traversing through said flowing sample fluid andproducing an output light traversing through an output window in saidsample cell; receiving said output light at two or more downholespectrometers; generating a plurality of measurement signals by said twoor more spectrometers based on said output light; and analyzing saidplurality of measurement signals to determine properties of said flowingsample fluid.
 17. The method for downhole fluid analysis defined inclaim 16 further comprising: providing input light from a plurality oflight sources wherein said plurality of light sources generate lightacross a wide spectral range.
 18. The method for downhole fluid analysisdefined in claim 16 further comprising: processing said input lightbefore introduction to said sample cell.
 19. The method for downholefluid analysis defined in claim 18, wherein said processing comprisesmodulating the amplitude of said input light.
 20. The method fordownhole fluid analysis defined in claim 18, wherein said processingcomprises modulating the frequency of said input light.
 21. A method fordownhole fluid analysis comprising: providing input light using at leastone light source generating an input light across a wide, continuousspectral range; inserting a sample fluid into a sample cell; introducingsaid input light to an input window of said sample cell, said lighttraversing through said sample fluid and producing an output lighttraversing through an output window in said sample cell; receiving saidoutput light at two or more downhole spectrometers; generating aplurality of measurement signals by said two or more spectrometers basedon said output light; and analyzing said plurality of measurementsignals to determine properties of said sample fluid; introducing saidinput light directly to said two or more spectrometers; generating aplurality of reference signals from said two or more spectrometers;calibrating said spectrometers using said plurality of referencesignals.